December 1995
DS36C278
Low Power Multipoint EIA-RS-485 Transceiver
General Description
Features
Y
100% RS-485 compliant
Ð Guaranteed RS-485 device interoperation
The DS36C278 is a low power differential bus/line trans-
ceiver designed to meet the requirements of RS-485 stan-
dard for multipoint data transmission. In addition it is com-
patible with TIA/EIA-422-B.
Y
Y
Low power CMOS design
I
500 mA max
CC
Built-in power up/down glitch-free circuitry
Ð Permits live transceiver insertion/displacement
DIP and SOIC packages available
The CMOS design offers significant power savings over its
bipolar and ALS counterparts without sacrificing ruggedness
against ESD damage. The device is ideal for use in battery
Y
Y
Y
b
a
40 C to 85 C
§
Industrial temperature range
§
powered or power conscious applications. I is specified at
CC
500 mA maximum.
On-board thermal shutdown circuitry
Ð Prevents damage to the device in the event of ex-
cessive power dissipation
The driver and receiver outputs feature TRI-STATE capa-
É
bility. The driver outputs operate over the entire common
Y
Y
Y
Y
Y
Y
b
a
7V to 12V
Wide common mode range
Receiver open input fail-safe
(/4 unit load (DS36C278)
(/2 unit load (DS36C278T)
ESD (human body model)
Drop in replacement for:
b
a
mode range of 7V to 12V. Bus contention or fault situa-
tions that cause excessive power dissipation within the de-
vice are handled by a thermal shutdown circuit, which forces
the driver outputs into the high impedance state.
²
t
128 nodes
t
64 nodes
t
2 kV
The receiver incorporates a fail safe circuit which guaran-
²
tees a high output state when the inputs are left open.
Ð LTC485, MAX485, DS75176, DS3695
The DS36C278T is fully specified over the industrial temper-
b
ature range ( 40 C to 85 C).
a
§
§
Connection and Logic Diagram
Truth Table
DRIVER SECTION
RE*
DE
DI
DO/RI
DO*/RI*
X
X
X
H
H
L
H
L
H
L
L
H
Z
X
Z
RECEIVER SECTION
RE*
DE
RI-RI*
RO
t
a
b
TL/F/12040–1
L
L
L
L
L
L
0.2V
0.2V
H
L
s
Order Number DS36C278TM, DS36C278TN,
DS36C278M, DS36C278N
See NS Package Number M08A or N08E
H
L
X
Z
H
²
OPEN
²
Note: Non-terminated, open input only
TRI-STATEÉ is a registered trademark of National Semiconductor Corporation.
C
1996 National Semiconductor Corporation
TL/F/12040
RRD-B30M36/Printed in U. S. A.
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Electrical Characteristics (Continued)
Over Supply Voltage and Operating Temperature ranges, unless otherwise specified (Notes 2 and 3)
Symbol
Parameter
Conditions
Reference
e a
Min Typ
Max Units
e
I
I
I
Line Input Current
(Note 7)
Other Input
e
0V,
DS36C278
V
12V
0
0
0
0
0
0
0
0
0.19 0.25
mA
IN
IN
e
4.75 to 5.25
DE
V
IL
, RE*
V ,
IL
e b
b
b
V
IN
7V
0.1
0.2
mA
mA
mA
mA
mA
mA
mA
e
V
CC
DS36C278T
e a
V
IN
12V
0.19
0.5
or 0V
e b
b
0.1
b
V
7V
0.4
IN
e a
IN
e
Line Input Current Glitch
(Note 7)
Other Input
e
0V,
DS36C278
V
12V
0.19 0.25
ING
e
3.0V or 0V,
DE
V
, RE*
V
,
IL
IL
e a
e
e b
b
b
V
7V
0.1
0.2
IN
e a
IN
V
T
CC
DS36C278T
V
12V
0.19
0.5
25 C
§
A
e b
b
0.1
b
V
IN
7V
0.4
e
g
Input Balance Test
RS
500X
(422) (Note 9)
400 mV
V
B
e b
e a
e a
e b
V
V
High Level Output Voltage
Low Level Output Voltage
Short Circuit Current
I
4 mA, V
0.2V
3.5
7
4.6
RO
OH
OH
ID
Figure 11
I
4 mA, V
0.2V
0.3
35
0.5
85
V
OL
OL
ID
e
e
I
I
V
GND
0.4V to 2.4V
mA
mA
OSR
OZR
O
O
RO
g
TRI-STATE Leakage Current
V
1
DEVICE CHARACTERISTICS
V
V
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
2.0
V
V
IH
CC
GND
0.8
2
V
IL
DE,
RE*,
DI
e
I
I
V
V
V
V
CC
mA
mA
mA
mA
mA
mA
mA
IH
IH
e
b
b
5V
2
2
IL
CC
CC
e
V
IL
0V
e a
3.0V
I
I
I
I
Power Supply Current
(No Load)
Driver and Receiver ON
200
200
200
200
500
500
500
500
CC
Driver OFF, Receiver ON
Driver ON, Receiver OFF
Driver and Receiver OFF
CCR
CCD
CCZ
V
CC
Switching Characteristics
Over Supply Voltage and Operating Temperature ranges, unless otherwise specified (Notes 3 and 8)
Symbol
Parameter
Conditions
Reference
Min
Typ
Max
Units
DRIVER CHARACTERISTICS
e
e
t
t
t
Differential Propagation
Delay High to Low
R
L
54X, C
L
100 pF
PHLD
PLHD
SKD
10
10
0
39
40
1
80
80
10
ns
ns
ns
Differential Propagation
Delay Low to High
Figures 5, 6
Differential Skew
b
t
t
PLHD
l
PHLD
l
t
t
t
t
t
t
Rise Time
Fall Time
3
25
25
80
80
50
65
50
50
ns
ns
ns
ns
ns
ns
r
3
f
e
Disable Time High to Z
Disable Time Low to Z
Enable Time Z to High
Enable Time Z to Low
C
15 pF
Figures 7, 8
Figures 9, 10
Figures 7, 8
Figures 9, 10
Ð
Ð
Ð
Ð
200
200
200
200
PHZ
PLZ
PZH
PZL
L
e
RE *
L
e
C
L
100 pF
e
RE *
L
3
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Switching Characteristics (Continued)
Over Supply Voltage and Operating Temperature ranges, unless otherwise specified (Notes 3 and 8)
Symbol
Parameter
Conditions
Reference
Min
Typ
Max
Units
RECEIVER CHARACTERISTICS
e
e
t
t
Propagation Delay
High to Low
C
15 pF
PHL
L
30
30
210
190
400
400
ns
ns
Figures 12, 13
Propagation Delay
Low to High
PLH
b
t
t
t
t
t
Skew, t
PHL
t
0
20
50
55
40
45
50
ns
ns
ns
ns
ns
SK
l
Output Disable Time
PLH
l
C
L
15 pF
Ð
Ð
Ð
Ð
150
150
150
150
PLZ
PHZ
PZL
PZH
Figures 14, 15, 16
Output Enable Time
Note 1: ‘‘Absolute Maximum Ratings’’ are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the devices
should be operated at these limits. The table of ‘‘Electrical Characteristics’’ specifies conditions of device operation.
Note 2: Current into device pins is defined as positive. Current out of device pins is defined as negative. All voltages are referenced to ground except V
OD1
and
V
OD2
.
e
a
e
a
Note 3: All typicals are given for: V
5.0V, T
25 C.
§
CC
A
Note 4: Delta
V
and Delta
V
are changes in magnitude of V and V , respectively, that occur when input changes state.
OD2 OC
l
OD2
l
l
OC
l
Note 5: Threshold parameter limits specified as an algebraic value rather than by magnitude.
e
b
Note 6: Hysteresis defined as V
HST
V
TH
V
TL
.
Note 7: I includes the receiver input current and driver TRI-STATE leakage current.
IN
Note 8: C includes probe and jig capacitance.
L
Note 9: For complete details of test, see RS-485.
Parameter Measurement Information
TL/F/12040–18
TL/F/12040–2
FIGURE 2. Driver V
OD3
FIGURE 1. Driver V
OD2
and V
OC
TL/F/12040–4
TL/F/12040–3
e b
FIGURE 4. Driver I
a
FIGURE 3. Driver V
OH
and V
OL
Vtest
7V to 12V
OSD
TL/F/12040–5
FIGURE 5. Driver Differential Propagation Delay Test Circuit
4
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Parameter Measurement Information (Continued)
TL/F/12040–6
FIGURE 6. Driver Differential Propagation Delays and Differential Rise and Fall Times
TL/F/12040–8
FIGURE 8. TRI-STATE Waveforms (t , t )
PZH PHZ
TL/F/12040–7
FIGURE 7. TRI-STATE Test Circuit (t , t )
PZH PHZ
TL/F/12040–10
FIGURE 10. TRI-STATE Waveforms (t , t )
PZL PLZ
TL/F/12040–9
FIGURE 9. TRI-STATE Test Circuit (t , t )
PZL PLZ
TL/F/12040–12
FIGURE 12. Receiver Differential Propagation Delay
Test Circuit
TL/F/12040–11
and V
OL
FIGURE 11. Receiver V
OH
5
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Parameter Measurement Information (Continued)
TL/F/12040–13
FIGURE 13. Receiver Differential Propagation Delay Waveforms
TL/F/12040–14
FIGURE 14. Receiver TRI-STATE Test Circuit
TL/F/12040–15
FIGURE 15. Receiver Enable and Disable Waveforms (t
, t )
PLZ PZL
TL/F/12040–16
FIGURE 16. Receiver Enable and Disable Waveforms (t
, t )
PHZ PZH
6
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Typical Application Information
TL/F/12040–17
FIGURE 17. Typical RS-485 Bus Interface
TABLE I. Device Pin Descriptions
Description
Pin No.
Name
t
1
RO
Receiver Output: When RE (Receiver Enable) is LOW, the receiver is enabled (ON), if DO/RI DO*/RI* by
s
200 mV, RO will be HIGH. If DO/RI DO*/RI* by 200 mV, RO will be LOW. Additionally RO will be HIGH for
OPEN (Non-terminated) Inputs.
2
3
4
RE*
DE
DI
Receiver Output Enable: When RE* is LOW the receiver output is enabled. When RE* is HIGH, the receiver
output is in TRI-STATE (OFF).
Driver Output Enable: When DE is HIGH, the driver outputs are enabled. When DE is LOW, the driver outputs
are in TRI-STATE (OFF).
Driver Input: When DE (Driver Enable) is HIGH, the driver is enabled, if DI is LOW, then DO/RI will be LOW
and DO*/RI* will be HIGH. If DI is HIGH, then DO/RI is HIGH and DO*/RI* is LOW.
5
6
7
8
GND
Ground Connection.
DO/RI
Driver Output/Receiver Input, 485 Bus Pin.
DO*/RI* Driver Output/Receiver Input, 485 Bus Pin.
Positive Power Supply Connection: Recommended operating range for V is 4.75V to 5.25V.
a
a
V
CC
CC
Unit Load
A unit load for an RS-485 receiver is defined by the input
a
b
b
at 0.25 mA for the top border and 7V at 0.2 mA for
the bottom border (see Figure 18 ).
current versus the input voltage curve. The gray shaded re-
b
a
gion is the defined operating range from 7V to 12V. The
a
The advantage of the (/2 UL and (/4 UL devices is the in-
creased number of nodes on one bus. In a single master
multi-slave type of application where the number of slaves
exceeds 32, the DS36C278/279/280 may save in the cost
of extra devices like repeaters, extra media like cable,
and/or extra components like resistors.
b
a
top border extending from 3V at 0 mA to 12V at 1 mA
is defined as one unit load. Likewise, the bottom border
a
b
b
extending from 5V at 0 mA to 7V at 0.8 mA is also
defined as one unit load (see Figure 18 ). An RS-485 driver
is capable of driving up to 32 unit loads. This allows up to 32
nodes on a single bus. Although sufficient for many applica-
tions, it is sometimes desirable to have even more nodes.
For example, an aircraft that has 32 rows with 4 seats per
row would benefit from having 128 nodes on one bus. This
would allow signals to be transferred to and from each indi-
vidual seat to 1 main station. Usually there is one or two less
seats in the last row of the aircraft near the restrooms and
food storage area. This frees the node for the main station.
The DS36C279 and DS36C280 have an additional feature
which offers more advantages. The DS36C279 has an auto-
matic sleep mode function for power conscious applica-
tions. The DS36C280 has a slew rate control for EMI con-
scious applications. Refer to the sleep mode and slew rate
control portion of the application information section in the
corresponding datasheet for more information on these fea-
tures.
The DS36C278, the DS36C279, and the DS36C280 all have
(/2 unit load and (/4 unit load (UL) options available. These
devices will allow up to 64 nodes or 128 nodes guaranteed
over temperature depending upon which option is selected.
The (/2 UL option is available in industrial temperature and
the (/4 UL is available in commercial temperature.
First, for a (/2 UL device the top and bottom borders shown
a
in Figure 18 are scaled. Both 0 mA reference points at 5V
and 3V stay the same. The other reference points are
b
a
for the bottom border (see Figure 18 ). Second, for a (/4 UL
a
b
b
12V at 0.5 mA for the top border and 7V at 0.4 mA
device the top and bottom borders shown in Figure 18 are
TL/F/12040–19
FIGURE 18. Input Current vs Input Voltage
Operating Range
a
scaled also. Again, both 0 mA reference points at 5V and
3V stay the same. The other reference points are 12V
b
a
7
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Physical Dimensions inches (millimeters)
8-Lead (0.150 Wide) Molded Small Outline Package, JEDEC
×
Order Number DS36C278TM, DS36C278M
NS Package Number M08A
9
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Physical Dimensions inches (millimeters) (Continued)
8-Lead (0.300 Wide) Molded Dual-In-Line Package
×
Order Number DS36C278TN, DS36C278N
NS Package Number N08E
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failure to perform, when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
2. A critical component is any component of
a
life
support device or system whose failure to perform can
be reasonably expected to cause the failure of the life
support device or system, or to affect its safety or
effectiveness.
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